JP2846673B2 - Method for producing zinc electrode for alkaline storage battery - Google Patents

Description

The present invention relates to a method for producing a zinc electrode for an alkaline storage battery using zinc as a negative electrode active material, such as a nickel-zinc storage battery and a silver-zinc storage battery.

(B) Conventional technology Zinc as a negative electrode active material has the advantages of high energy density per unit weight, low cost, and non-polluting. It has features such as high energy density and high operating voltage, and is expected to be a secondary battery.

However, in this type of alkaline storage battery, when the charge / discharge cycle is repeated, zinc is eluted in the alkaline electrolyte at the zinc electrode during discharging to form zincate ions, and the zincate ions are dendritic on the surface of the zinc electrode during charging. Alternatively, it is deposited in a spongy manner. As a result, the electrodeposited zinc penetrates through the separator to cause an internal short circuit due to the repetition of the charge / discharge reaction, or the shape of the zinc electrode is deformed to reduce the reaction area, thereby deteriorating the battery characteristics. As a method of preventing such a shape deformation of the zinc electrode or crystal growth of dendritic zinc, for example,
JP-A-52-19685 and JP-A-59-189562 have a larger hydrogen overvoltage than zinc such as indium and thallium,
There is also a method of adding an additive whose oxidation-reduction potential is more noble than zinc.

However, simply by dry mixing, the effect of the additive is not sufficiently exhibited because the dispersibility of the additive is poor. In particular, at the beginning of the charge / discharge cycle in which the additive is not sufficiently distributed, the dendritic zinc crystal tends to grow at the time of charging, and the initial failure rate is large. For this reason,
In JP-A-63-158749 and JP-A-63-158750, an additive is retained in zinc added as a discharge reserve at the time of manufacturing an electrode to improve dispersibility. However, since the starting material zinc has a very large particle size as compared with zinc oxide, it tends to become the nucleus of dendritic zinc crystal growth during charging, and if the amount of addition is increased, the dendritic zinc crystal tends to grow. The addition amount can be only 10% by weight to 50% by weight based on zinc oxide. For this reason, there is a problem that the dispersion of the additive is insufficient, the effect cannot be sufficiently exhibited, and initial failure due to dendrite short-circuit occurs during quick charging.

(C) Problems to be Solved by the Invention If zinc powder holding an additive is used, the dispersibility of the additive is improved, so that the defective rate at the initial stage of the charge / discharge cycle can be reduced, and during the rapid charging, Although the effect of suppressing dendritic zinc crystal growth is recognized, it cannot be completely prevented.

The present invention has been made in view of such a problem, and proposes a method for producing a zinc electrode capable of improving the dispersibility of an additive in the zinc electrode. In addition, the present invention provides an alkaline storage battery having excellent cycle characteristics by sufficiently exhibiting the effect of the additive and suppressing crystal growth of dendritic zinc from the zinc electrode.

(D) Means for Solving the Problems In the method for producing a zinc electrode for an alkaline storage battery according to the present invention, a method of adding a zinc powder and a zinc oxide powder containing an element having a larger hydrogen overvoltage and a noble redox potential than zinc to zinc powder. After the surface is modified or added to the surface by adding the respective agents, the zinc powder and the zinc oxide powder are mixed and held on the conductive core.

The form of the additive may be any of metal, oxide, and hydroxide.

(E) Action When the charge / discharge cycle is repeated using an alkaline storage battery provided with a zinc electrode, zinc is eluted into the alkaline electrolyte during charging to become zincate ions. Then, during charging, the zincate ions are deposited on the surface of the zinc electrode in a dendritic or sponge form, and the repetition of this charge / discharge reaction causes the deposited zinc to penetrate the separator, causing an internal short circuit or the shape of the zinc electrode. Are deformed, the reaction area is reduced, and the battery characteristics deteriorate.
Therefore, if an additive having a higher hydrogen overvoltage and a noble redox potential than zinc such as indium and thallium is added, the overvoltage of zincate ion deposition can be increased, thereby preventing dendrite short circuit and initial failure. The rate can be reduced. However, in the method in which the additive powder and the zinc active material powder are simply dry-mixed, or the zinc electrode is prepared by holding the additive in zinc, the dispersibility of the additive in the zinc electrode in the early charge / discharge cycle is poor. At the time of quick charging, there is a disadvantage that the initial failure rate due to dendrite short-circuit increases. Therefore, as in the present invention, to each of the zinc powder and the zinc oxide powder, an additive that contains an element having a higher hydrogen overpotential than zinc and a redox potential noble than zinc is added to modify or modify the surface. After adding to the mixture, by mixing, when viewed microscopically, the action of the additive increases the overpotential of the electrodeposition reaction of the zincate ion, and as a result, the zincate ion Electrodeposition can occur slowly and uniformly. Therefore, the growth of dendritic zinc crystals from the zinc electrode is effectively prevented.

When viewed macroscopically, the additive is uniformly present in the vicinity of the active material constituent particles, zinc oxide and zinc. And the cycle characteristics are not deteriorated even when quick charging is performed.

(F) Examples Hereinafter, reference will be made to a comparison between examples of the present invention and comparative examples,
It will be described in detail.

[Example] Zinc powder was immersed in a 0.1 mol / l indium chloride aqueous solution, stirred for 30 minutes, added with a 0.1 mol / l potassium hydroxide aqueous solution, and then thoroughly washed with water, and surface modified with indium added. A zinc powder (zinc powder) was obtained. The weight of the substituted indium at this time was about 2% by weight of the weight of zinc. Next, after the zinc oxide was sufficiently immersed in an aqueous solution of indium nitrate, water was removed to add indium nitrate to the surface of the zinc oxide. Further, the substrate was treated with a dilute alkali to convert indium nitrate added to the surface into indium oxide, and indium oxide was added. This was used as zinc oxide powder. The zinc powder and zinc oxide powder thus obtained were dry-mixed at a weight ratio of 1: 2.

Next, water was added to the mixed powder composed of 95% by weight of the zinc active material and 5% by weight of the fluororesin, and kneaded to obtain a paste. The paste was pressed on a conductive core made of punched metal to form a zinc electrode. This zinc electrode is combined with a well-known sintered nickel electrode to form a cylinder-sealed nickel-nickel with a nominal capacity of 500 mAh.
A zinc storage battery was obtained. This battery was designated as Battery A of the present invention.

[Comparative Example 1] Zinc oxide and zinc in the zinc active material in the above example,
A zinc electrode was obtained in the same manner as in the above example, except that the zinc oxide, zinc, and indium hydroxide were dry-mixed so that the molar ratio of indium was the same as that of the indium. The zinc oxide and zinc do not contain any additives.

[Comparative Example 2] Zinc oxide, zinc in the zinc active material in the above example,
A zinc electrode was obtained and a battery was assembled in the same manner as in the above example except that zinc, the surface-modified zinc oxide containing indium, and indium hydroxide were mixed so as to have the same molar ratio of indium. Comparative battery C was obtained. This zinc contains no additives.

[Comparative Example 3] Zinc oxide, zinc in the zinc active material in the above example,
A zinc electrode was obtained and the battery was assembled in the same manner as in the above example except that the surface-modified zinc containing indium, zinc oxide, and indium hydroxide were mixed so that the molar ratio of indium was the same as that of indium. Comparative battery D was used. In addition, this zinc oxide does not contain an additive.

Using the batteries A, B, C, and D thus obtained, comparison of charge / discharge cycle characteristics was performed. The cycle conditions at this time were as follows: after charging each battery with a charging current of 1000 mA for 0.5 hour,
The battery was discharged at a charge current of 00 mA until the battery voltage reached 1.4 V, and charging and discharging were repeated until the battery capacity reached 350 mAh.

 The result is shown in FIG.

Meanwhile, the initial failure rate of each battery was examined. The initial failure rate is
It is calculated from the initial number of defective cells in 20 cells under the same conditions when the number of charge / discharge cycles has elapsed 20 times.

 The results are shown in Table 1.

As apparent from FIG. 1 and Table 1, the battery A of the present invention was used.
It is understood that the test sample has an extremely low initial failure rate and excellent cycle characteristics as compared with the comparative batteries B, C, and D.

In this embodiment, as a method of modifying the surface or adding to the surface by adding a metal as an additive to zinc powder,
Although an ion exchange reaction was used, the same effect can be obtained by using a powder obtained by spraying a eutectic of zinc and another metal. As a method for modifying or adding a surface to the surface by adding an additive of another metal to zinc oxide, other than a method using a solution of a salt of another metal, an electroless plating method, a vapor deposition method, or the like can be considered. Needless to say, the same effect can be obtained for these.

Also, an example of indium was shown as an additive to be added to zinc or zinc oxide. However, as long as the element has a redox potential nobleer than zinc and a hydrogen overpotential larger than zinc, it is in the form of a metal or a compound thereof. Even if there is, the same effect can be expected. As an element to be contained in the additive, thallium, tin, bismuth, cadmium and the like can be used in addition to indium.

(G) Effect of the Invention According to the method for producing a zinc electrode for an alkaline storage battery of the present invention, the dispersibility of the additive in the zinc electrode is improved, the effect of the addition is sufficiently exerted, and the initial failure caused by dendritic zinc growth. The rate can be kept extremely low, and an alkaline storage battery having excellent cycle characteristics can be provided, so that its industrial value is extremely large.

[Brief description of the drawings]

 FIG. 1 is a comparison diagram of cycle characteristics of a battery. A: battery of the present invention, B, C, D: comparative battery.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-63-1558749 (JP, A) JP-A-63-158750 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01M 4/24-4/26 H01M 4/42 H01M 4/62

Claims (1)

(57) [Claims] (1) After adding an additive containing an element having a larger hydrogen overpotential than zinc and a noble redox potential to zinc powder and zinc oxide powder to modify or add the surface to the surface, A method for producing a zinc electrode for an alkaline storage battery, comprising mixing zinc powder and the zinc oxide powder and holding the mixture on a conductive core.